A variety of copolymers are known as copolymers of (meth)acrylic acid and alkyl(meth)acrylate, which are used in thickening agents for cosmetics and the like; moisturizers for cataplasms and the like; emulsifiers; suspension stabilizers for suspensions; and the like. For example, a copolymer obtained by reacting a specific amount of olefin-based unsaturated carboxylic acid monomers and a specific amount of alkyl(meth)acrylate (a carbon number of the alkyl group is 10-30) (See Patent Document 1), a copolymer obtained by reacting a specific amount of olefin-based unsaturated carboxylic acid monomers and a specific amount of alkyl(meth)acrylate (a carbon number of the alkyl group is 10-30) and a cross linking agent (See Patent Document 2), a copolymer obtained by reacting olefin-based unsaturated carboxylic acid monomers and alkyl(meth)acrylate (a carbon number of the alkyl group is 8-30) (See Patent Document 3) and the like are known.
These copolymers of (meth)acrylic acid and alkyl (meth)acrylate are used in the above applications usually after dissolving into water and the like and neutralize with alkali to form a neutralized viscous liquid at a concentration of about 0.1 to 1 weight %.
This neutralized viscous liquid had a problem that their viscosity or transmittance reduces and a part of the copolymer precipitates when electrolytes used as various raw materials for products or additives coexist even at relatively low concentrations.
In particular, recently, in a field of cosmetics and the like, cosmetics containing high amounts of minerals and the like in order to differentiate from other products as well as various properties, for example, good appearances such as transparency, non-sticky texture and the like are in the spotlight. Therefore, it is desired to invent a thickening agent which can form a neutralized viscous liquid having a high viscosity and a high transmittance even in the presence of a relatively high concentration of electrolytes.
In addition, from a viewpoint of reducing manufacturing costs, it is desired to invent a thickening agent having properties leading to improvement in manufacturing efficiencies in a variety of manufacturing processes.    [Patent Document 1] JP 6190/1976A    [Patent Document 2] JP 232107/1984A    [Patent Document 3] U.S. Pat. No. 5,004,598